1. Field of the Invention
The present invention relates to a data collection system for electric discharge machines in which a computer is connected with electric discharge machines over a network.
2. Description of the Related Art
A known technique for assessing the quality of a machined product manufactured by machining with an electric discharge machine is to measure and assess the surface roughness or dimensional accuracy of the machined product after machining. However, general assessing method of the quality of a machined product is to obtain monitoring information, such as machining voltage, machining current and machining speed which are used for keeping track of machining conditions during machining, and to asses the obtained monitoring information by determining the monitoring information falls within a prescribed range or not. And such obtained monitoring information is stored in a storage device in a numerical controller mounted on the electric discharge machine or transferred to a computer over a network when the electric discharge machine is connected to a network.
Japanese Patent No. 4137384 (JP4137384B2) discloses a technique for collecting data on machining speed, machining voltage, machining current, on-time and off-time of voltage applied to electrodes, total number of discharges, the number of abnormal discharges, abnormal discharge rate and discharge frequency during machining with an electric discharge machine, and storing the collected data in a numerical controller mounted on the electric discharge machine.
Such a numerical controller mounted on an electric discharge machine, however, typically has a smaller data storage capacity than a personal computer or a server. This makes it difficult to store multiple kinds of monitoring information over all routes of electric discharge machining that takes a long machining time in terms of storage capacity. Also, mounting a large-capacity storage device on an electric discharge machine for storing various kinds of monitoring information increases costs of the electric discharge machine.
Another known technique is to continuously transfer various kinds of monitoring information to a network-connected computer and store the information in a storage device in the computer, instead of storing them in the numerical controller mounted on the electric discharge machine. While this scheme avoids the problem of increase in costs of the electric discharge machine caused by mounting a large-capacity storage on the electric discharge machine as in the case of the above-mentioned patent document, constant transfer of data over a network can increase communication load on the network or result in monitoring information not being stored in the computer in the event of a failure on the network.
Japanese Patent No. 4047544 (JP4047544B2) discloses a system for collecting monitoring information such as variations in machining voltage and/or machining speed during machining via a network connection between a computer and an electric discharge machine.
The system, constituted by a computer and an electric discharge machine, is able to store monitoring information such as machining speed, machining voltage, and machining current during a machining process in the numerical controller in the electric discharge machine at predetermined time intervals and subsequently transmit the information to an external computer or the like as needed. This scheme, however, has the disadvantage of data volume becoming large because it stores monitoring information at predetermined time intervals.